NO. 1)77. NORTH AMERICAN LEPTONACEA— BALL. 893 



colored zoues; beaks distinct, ofteu eroded, ends and base rounded, 

 valves moderately convex, teeth strong in the right valve, anterior 

 adductor scar narrow and rather irregular, elongated, posterior 

 rounded, pallia! scar linear. Lon. 4.3, alt. 3.3, diam. 2 mm. 



Kesembles M, tumida Carpenter, but is juore ovate and with less 

 prominent beaks and smaller resilium. 



MYSELLA PEDROANA Dall. 



Mysella pedroana, new species. 



(Plate LXXXVIII, &g. 4.) 



B. 21. Shell large, thin, rounded, rather compressed, white, with a 

 concentrically rugose pale-brownish epidermis (to which, in the type, 

 adheres a good deal of blackish oxide of iron); beaks inconspicuous; 

 surface with coarse, concentric, incremental lines; inequilateral; the 

 posterior side short, dorsal margins merging roundly into the distal 

 and they into the basal margin, which last is nearly straight; hinge 

 feeble, the right anterior lamella elongated and very slender, the pos- 

 terior one shorter and stouter, the resilium subumbonal and very 

 small; adductor scars small, the pallial scar linear. Lon. 9, alt. 7.3, 

 diam. 3 mm. 



This is an unusually large and fragile species, of which a single shell 

 was found on the beach at San Pedro. 



MONTACUTA FLORIDANA Dall. 



Montacuta floridana, uew species. 



(Plate LXXXVII, fig. 10.) 



A. 28. Shell subovate, inequilateral, posterior end much the shorter, 

 white, inflated; beaks low, polished; sculpture of concentric lines 

 growing gradually stronger downward and forward until on the lower 

 anterior third they form low, stout, evenly distributed, concentrically 

 striated lamellse, remaining feebler on the rest of the shell; base nearly 

 straight, dorsal margin convexly arcuated, ends evenly rounded; hinge 

 with a prominent slender cardinal in each valve, the lamellae obsolete; 

 sockets of the resilium thickened and raised above the inner surface of 

 the valve. Lon. IG, alt. 10, diam. 9.5 mm. 



This is probably the largest species of the genus, if, indeed, it should 

 not prove eventually distinct from the typical forms upon which the 

 genus rests. The anterior lamellic are entirely absent and there is no 

 radial sculpture visible without a lens. A few faint striatious on the 

 anterior slope are feebly reflected on the inner surface of the anterior 

 margin. 



The recent specimens of this species were first collected on the 

 beaches of west Florida, near the Manatee River, by Charles T. 

 Simpson. 



